Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and a rotor. The rotor typically includes a rotatable hub having one or more rotor blades attached thereto. A pitch bearing is typically configured operably between the hub and the rotor blade to allow for rotation about a pitch axis. The rotor blades capture kinetic energy of wind using known airfoil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
Changes in atmospheric conditions, for example, wind speed, wind turbulence, wind gusts, wind direction, and/or air density may significantly influence power produced by the generator. More specifically, a power output of the generator increases with wind speed until the wind speed reaches a rated wind speed for the turbine. At and above the rated wind speed, the generator operates at rated power. The rated power is an output power at which the generator can operate with a level of fatigue or extreme load to turbine components that is predetermined to be acceptable. At wind speeds higher than a certain speed, typically referred to as a “trip limit,” the wind turbine may implement a control action, such as shutting down or de-rating the wind turbine in order to protect wind turbine components from damage.
Conventional systems and methods for controlling wind turbines during such transient wind conditions utilize one or more sensors positioned on the wind turbine to detect wind conditions. For example, a wind speed sensor positioned on the wind turbine measures a wind gust at substantially the same time as the wind gust strikes the rotor blades. As such, wind turbine operation adjustments are subject to a time lag between measurement of the wind gust and the control action. As a result, the wind gust may cause rotor acceleration that will create excessive turbine loading and/or fatigue. In some instances, the wind gust may cause the rotor speed or power output to exceed a trip limit, before a wind turbine operation adjustment is completed, causing the wind turbine to be shut down.
Modern systems and methods for controlling wind turbines utilize upwind measuring sensors, such as Light Detecting and Ranging (LIDAR) sensors, to address the aforementioned time lag. As such, a change in wind acceleration may be measured upwind from the wind turbine, and the control action may be preemptively adjusted to compensate for the change in wind speed once the wind reaches the wind turbine.
Typically, LIDAR sensors operate by scattering radiation from natural aerosols (dust, pollen, water droplets, etc.) and measure the Doppler shift between the outgoing and incoming radiation. Thus, to measure the wind speed and direction upwind of the wind turbine, the LIDAR sensor scans the wind vector, typically using a conical scan, such that the vector can be intersected at a range of angles, thereby enabling the true (3D) velocity vector to be deduced. Sequential switching of fiber optic-based laser signals in the optical chain of the LIDAR sensor is commonly applied to develop different beam line of sight measurements of wind vectors in front of the wind turbine rotor. This is common to both pulsed Doppler and continuous wave LIDAR systems applied in application.
LIDAR sensors are mounted on the wind turbine in such a manner to minimize interference with the wind turbine structures that would occlude the laser beam path. However, when LIDAR sensors are mounted on the nacelle, rotor rotation can result in partial blocking of the LIDAR beam signals. This impact can be significant, e.g. reducing the beam signal availability to 30% to 60% due to this geometric effect. Thus, certain control systems apply signal averaging and/or selective signal applications for wind turbines utilizing LIDAR measurements to reduce the blocking impact of the rotor blades as the hub rotates. Such control systems, however, substantially reduce the LIDAR signal availability and the quality of the wind field assessments of impinging wind vectors.
In view of the aforementioned, an improved system and method for improving signal availability of LIDAR sensors mounted on a nacelle of a wind turbine would be desired in the art. Thus, the present disclosure is directed to sequencing LIDAR sensor beam signals with the rotor position of a wind turbine so as to improve signal availability.